1. Field of the Invention
This application relates to resistant starch with improved processability and a method of preparing the same. More particularly, this application relates to resistant starch having a predetermined content of total dietary fiber and also improved processability such as dough-forming ability at the same time. In addition, this application relates to a method of preparing resistant starch, of which water holding capacity can be increased by regulating factors such as water injection volume, heat, and pressure, at the time of the extrusion of modified starch that is modified by a cross-linked bond.
2. Description of the Related Art
Starch is a human's main source of carbohydrates and is used as our energy source by decomposing it to glucose through an action of digestive enzyme in a small intestine, and then absorbing the glucose into blood.
Generally, starch is classified into three types, i.e., rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) depending on a type of digestion in a small intestine (Englyst et al., Classification and measurement of nutritionally important starch fractions. European Journal of Clinical Nutrition 46:33-50, 1992).
Among them, the resistant starch is largely divided into four groups according to their types—specifically, RS 1-type that is physically impossible to access; RS 2-type that has a B-type crystal form as raw starch particles, and resistance to α-amylase; RS 3-type that is formed via the aging process; and RS 4-type that has enzyme resistance by a chemical modification.
Many studies have been done on the physiological advantages of resistant starch having the four types as mentioned above. The resistant starch has various effects in that it has the physiological activity similar to oligosaccharides and dietary fibers; is not digested and absorbed in a small intestine; slowly increases blood sugar levels after meals; prevents colorectal cancer, hypertension, hyperlipidemia, and the like by allowing microorganisms to produce short chain fatty acids in a large intestine; inhibits accumulation of fat; and the like. The resistant starch that has the effect disclosed above and also functions as a source of dietary fiber may be useful as a food material.
Meanwhile, the RS 4-type resistant starch having enzyme resistance by a chemical modification is prepared by the techniques of various known methods of preparing (Modified starches: Properties and Uses, Ed. Wurzburg, CRC Press, Inc., Florida, 1986). A method of preparing the RS 4-type resistant starch includes a cross-linking reaction, esterification, eterification, conversion, and the like. More specifically, the resistant starch prepared by the cross-linking reaction includes modified starch, and the like, modified by a cross-linking agent, for example, sodium trimetaphosphate (STMP), phosphoryl chloride, adipic acid anhydrous, and the like; the resistant starch prepared by the esterification includes phosphated starch, acetylated starch, octenyl succinate substituted starch, and the like; and the resistant starch prepared by the eterification includes hydroxypropylated starch, and the like. In addition, the resistant starch prepared by the conversion modification includes acid hydrolyzed starch, the starch oxidized by sodium hypochlorite, the starch modified by enzyme, and the like. The above methods may be used individually or in combination.
Especially, since the material of the resistant starch prepared by the cross-linking reaction has the advantages of a relatively high content of total dietary fiber and an improvement in quality at the time of manufacturing foods, new techniques for an application of the above material to foods have been developing. However, there are several problems that the resistant starch prepared by the conventional cross-linking reaction is lacking in absorption ability of water at the time of the food processing, such as a mixing of the starch itself and water to make dough, a mixing with the flour to make dough, and the like thereby interrupting the dough formation, and the resistant starch is present in a type similar to raw starch particles without a modification of starch particles thereby giving a feeling of irritation to a final product.